feature: add server random and master key fetch api

[theweakgod]

What

Add two new FFI-based Lua APIs to the ngx.ssl module:

• get_server_random([outlen]) — returns the server random (default 32 bytes) from the current SSL connection, wrapping OpenSSL's SSL_get_server_random().
• get_session_master_key([outlen]) — returns the master secret (default 48 bytes, i.e. SSL_MAX_MASTER_KEY_LENGTH) from the current SSL session, wrapping OpenSSL's SSL_SESSION_get_master_key().

Both follow the same calling convention as the existing get_client_random(): pass 0 to get the length, pass nil or omit to get the value with the default size.

Why

The ngx.ssl module already exposes get_client_random(), but server random and master key are missing. All three are required to produce an NSS Key Log entry:

CLIENT_RANDOM <client_random_hex> <master_key_hex>

This file format is supported by Wireshark for decrypting TLS 1.2 traffic captures. Without this PR, users have to resort to LD_PRELOAD hacks, eBPF tools, or NGINX Plus (ssl_key_log / proxy_ssl_key_log directives) to obtain the same data.

Usage

local ssl = require "ngx.ssl"
 
local cr = ssl.get_client_random()   -- 32 bytes raw
local sr = ssl.get_server_random()   -- 32 bytes raw
local mk = ssl.get_session_master_key() -- 48 bytes raw

Produce a Wireshark-compatible key log line:

local to_hex = require "resty.string".to_hex
local line = "CLIENT_RANDOM " .. to_hex(cr) .. " " .. to_hex(mk) .. "\n"

[zhuizhuhaomeng]

This feature has been merged